Digital multimedia broadcasting, known under the abbreviation of DMB, is an extension of previous digital audio broadcasting, known under the abbreviation of DAB, by audiovisual contents. Digital multimedia broadcasting, DMB, “inherits” full DAB functionality, but is supplemented by the possibility of additionally transmitting MPEG2-encoded transport streams comprising video contents and/or audio contents.
At the transmitting end, the existing DAB multiplexer is supplemented, for this purpose, by a DMB gateway accepting the MPEG2 transport stream from a DMB encoder.
FIG. 14 shows a schematic representation of DMB signal processing. DMB signal processing 1400 of FIG. 14 receives multimedia information 1410 including, e.g., an audio signal and/or a video signal. DMB signal processing 1400 further includes a DMB encoder 1420 configured to create an MPEG2 transport stream 1422 on the basis of the multimedia information 1410. Signal processing 1400 further includes a DMB gateway 1430 configured to receive the MPEG2 transport stream 1422 and to create a DAB subchannel 1432 on the basis thereof. Signal processing 1400 further includes a DAB multiplexer 1440 configured to add the DAB subchannel 1432 to a DAB signal which combines, for example, a plurality of DAB subchannels. Thus, a DAB multiplex signal is obtained, for example.
For details of how a signal conforming to DMB, or a DAB signal including DMB information, may be obtained please refer to the corresponding publications of the European Broadcasting Union (EBU), for example. Details are given, for example, in the publication ETSI TS 102 428, VI.2.1 entitled “Digital Audio Broadcasting (DAB); DMB video services; User application specification” and in the documents referred to therein.
Digital multimedia broadcasting, DMB, is a technology by means of which “television” on mobile receivers is to be enabled. Thus, DMB represents an alternative to technologies such as DVB-H, for example.
One application of interest is pay TV, wherein contents are transmitted in a protected (encrypted) manner and are available to entitled users only. This concept will be referred to as access restriction below. Encryption of the contents and provision of useful additional messages is performed by a system for conditional access, which is sometimes also referred to as a “Conditional Access System”, or “CA” for short. For example, the additional messages are entitlement messages (also referred to as “EMM”) or messages containing the current content key (also referred to as ECM). Entitlement messages are sometimes also referred to as entitlement management messages EMM. Messages containing a current content key are sometimes also referred to as entitlement control messages ECM. The additional messages will be referred to as CA information for short in the following and are also transmitted via the broadcasting channel. One goal is to keep the overhead, which results from the CA information (information on conditional access) being sent out, to a minimum.
Against this background, it is the object of the present invention to provide a concept which enables efficiently transmitting access-restricted media information (at a low consumption of resources).